The present invention relates to a panel grounding electrode and a display device, and more particularly, to a grounding electrode for providing electrical connection between a conductive coat and a grounding member such as a reinforcing band or a frame, the conductive coat having a low-reflection antistatic function or an unwanted radiation electric field leakage preventing function and being formed on a surface of a display area of a panel which constitutes an image display device such as a color cathode ray tube or a liquid crystal display panel, as well as to a display device which has an antistatic function or an unwanted radiation electric field leakage preventing function using such a grounding electrode.
There are image display devices such as various kinds of cathode ray tubes including color cathode ray tubes and flat panel displays including liquid crystal panels and cold cathode panels. Such an image display device has a conductive coat coated on at least the surface of its display area which constitutes its screen, for the purpose of preventing electrical-shock accidents or attraction of dust to its surface from being caused by static electricity which occurs on its display surface, or for the purpose of preventing an unwanted radiation electric field from leaking to the outside.
This conducive coat ordinarily has a low-reflection layer on its outermost surface and is also called a low-reflection antistatic film. The conductive coat prevents reflection of external light on the panel, and is electrically connected to grounding members of the device so that static electricity occurring due to the operation of the device is not accumulated in the conductive coat.
For example, a color cathode ray tube includes a vacuum envelope (glass bulb) which is made of a panel having phosphors, a neck which houses an electron gun, and a funnel which connects the panel and the neck, and provides image display by causing electron beams to scan the phosphor film applied to the inner surface of the panel. In the color cathode ray tube, a high-voltage anode voltage is applied to the phosphor film. For this reason, static electricity is induced on the surface of the panel and is accumulated at a high potential, and this static electricity gives adverse influences such as giving an electric shock to a user and attracting surrounding dust to degrade the quality of display images. In addition, there is a likelihood that the low-reflection antistatic film may be destroyed by a high-voltage electric field (unwanted radiation electric field) radiated during the operation of the display device or by discharge accompanying the on/off operation of its power source.
For this reason, the conductive coat is coated onto the surface of the panel, and is electrically connected to a reinforcing band which is a grounding member held at ground potential, by using a conductive member such as metal tape or conductive rubber.
Similarly, in a flat panel display such as a liquid crystal panel, a conductive coat coated on its panel is electrically connected to a frame positioned at the periphery of its display area, by using a conductive member similar to the aforementioned one.
The manner of conductive connection between the panel and the grounding member will be described below with reference to a color cathode ray tube by way of example.
FIG. 7 is a schematic view of the front of a panel portion of a color cathode ray tube, aiding in explaining the essential construction of the color cathode ray tube whose panel has a surface coated with a conductive coat, while FIG. 8 is a schematic side view of the entire color cathode ray tube.
In FIGS. 7 and 8, reference numeral 1 denotes a panel which forms a screen serving as a display area, and the panel 1 has a surface coated with an antireflection film as well as a conductive coat 2 for preventing static charging and for preventing an unwanted radiation electrical field. Reference numeral 60 denotes a grounding tape (metal tape) made of a metal foil which serves as a grounding electrode. Reference numeral 4 denotes a reinforcing band for preventing implosion, which is tightly wrapped around the vicinity of a portion in which the panel 1 and a funnel are sealed together. Reference numeral 10 denotes a mounting support (lug or bracket) which is provided at each required position on the reinforcing band 4. Reference numeral 11 denotes a neck which houses an electron gun. Reference numeral 12 denotes a funnel portion which connects the panel 1 and the neck 11.
The surface of the panel 1 is coated with the conductive coat 2 made of a transparent conductive material, and the grounding tape (metal tape) 60 is stuck to both the conductive coat 2 and the reinforcing band 4 so that the conductive coat 2 is electrically connected and grounded to the reinforcing band 4 (for example, Japanese Patent Laid-Open No. 174945/1992).
The conductive coat 2 has a surface resistance of approximately 10-100 kxcexa9/xe2x96xa1 so that unwanted radiation electric fields leaking from the panel 1 can be reduced. For this reason, in the related art, in the case where the grounding tape 60 made of a metal foil is used as a grounding electrode, a discharge phenomenon occurs at the interface between the conductive coat 2 and the grounding tape 60 and the destruction of the conductive coat gradually proceeds, so that the reliability of electrical conduction is impaired.
Accordingly, to inhibit the destruction of the conductive coat, the conductive coat and the reinforcing band are connected together by a silicone resin which contains a conductive filler, instead of by the metal-foil grounding tape (Japanese Patent Laid-Open No. 83434/1990), or the conductive coat is subjected to ultrasonic soldering and the obtained solder portion and the reinforcing band are connected together by a conductive material such as metallic wire (Japanese Patent Laid-Open No. 286229/1989).
As described above, the construction in which the metal-foil grounding tape is used to provide connection between the conductive coat and the reinforcing band can realize a high work efficiency during its manufacturing process. However, in the case where the conductive coat has a multi-layer structure in which its outermost layer is an insulator, its electrical conduction becomes unstable. In the case of a conductive coat having a surface resistance of 100 kxcexa9/xe2x96xa1 or less, the destruction of the conductive coat due to discharge occurs.
In the case where the silicone resin (conductive silicone) which contains a conductive filler is used to connect the conductive coat and the reinforcing band, the destruction of the conductive coat due to discharge can be inhibited so that electrical conduction can be effectively ensured. However, the conductive silicone has the problems that its curing time after application is long and its handling until curing is not easy, and that its adhesion to the conductive coat after curing is good but the conductive silicone is difficult to remove during a recycle process and is inferior in work efficiency.
Furthermore, in the case of silicone having a high resistivity, in an antistatic film which includes a conductive coat having a surface resistance of several hundred xcexa9/xe2x96xa1 and is provided with a low-reflection function, it is impossible to fully utilize the low-resistance characteristic of the conductive coat, so that it is impossible to reduce leakage unwanted radiation electric fields which are minute alternating potentials.
Even in the method of subjecting the conductive coat to ultrasonic soldering and connecting the obtained solder portion and the reinforcing band together by a conductive material such as metal-foil grounding tape, if the surface resistance of the conductive coat is several hundred xcexa9/xe2x96xa1, the destruction of the conductive coat due to discharge occurs, and the conductive silicone is difficult to remove even during a recycle process.
Incidentally, the above description is not limited to color cathode ray tubes and similarly applies in various kinds of displays such as liquid crystal panels.
Other documents which disclose related arts associated with the above-described ones are Japanese Patent Laid-Open Nos. 149108/1998, 129159/1997, 214579/1998, 233180/1998 and 82434/1990.
A representative object of the invention is to provide a panel grounding electrode which prevents the destruction of its conductive coat due to discharge and highly efficiently reduces the leakage of unwanted radiation electric fields, and which is high in the work efficiency with which the conductive coat and a grounding member are electrically connected together, as well as to provide an image display device which includes the panel grounding electrode.
To achieve the above object, the invention uses a conductive adhesive material having conductivity in the whole of an adhesive layer, as means (panel grounding electrode) for providing connection between the conductive coat and the grounding member. Representative aspects of the invention will be described below.
First, regarding a panel grounding electrode which provides connection between a conductive coat and a grounding member,
(1) the grounding member is disposed outside a display area of a panel having a conductive layer on its surface and an insulating layer on the conductive layer, and the panel grounding electrode for electrically connecting the conductive layer and the grounding member in a peripheral portion of the display area includes a conductive adhesive material having conductive in the whole of an adhesive layer. The conductive adhesive material having conductivity in the whole of the adhesive layer makes use of conductivity based on a so-called xcfx80 electron conduction theory.
(2) In Paragraph (1), an adhesive insulating protective tape is provided on the surface of the conductive adhesive material opposite to a surface thereof which adheres to the panel.
(3) In Paragraph (2), a metal-evaporated tape is provided between the conductive adhesive material and the insulating protective tape.
(4) In Paragraphs (1) to (3), the conductive adhesive material uses a silicone-based adhesive material into which is kneaded a silicone-based resin in which carbon particulates are dispersed.
(5) In Paragraphs (1) to (3), the conductive adhesive material uses an acrylic-based adhesive material into which is kneaded a silicone-based resin in which carbon particulates are dispersed.
According to the above-described construction, it is possible to provide a grounding electrode which ensures a good work efficiency and a stable electrical conduction. In addition, regarding an image display device using the above-described panel grounding electrode,
(6) the image display device includes a grounding member disposed outside a display area of a panel coated with a conductive coat, and a panel grounding electrode for electrically connecting the conductive coat to the grounding member in a peripheral portion of the display area, and the panel grounding electrode includes a conductive adhesive material.
(7) In Paragraph (6), the panel grounding electrode has an adhesive insulating protective tape on the surface of the conductive adhesive material opposite to a surface thereof which adheres to the panel, and at least part of the insulative protective tape is adhered to either one or both of the panel and the grounding member beyond the conductive adhesive material.
(8) In Paragraph (7), a metal-evaporated tape is provided between the conductive adhesive material and the insulating protective tape.
According to the above-described constructions, it is possible to provide an image display device provided with an antistatic function or an unwanted radiation electric field leakage preventing function.
The invention is not limited to any of the above-described constructions nor any of the constructions of embodiments which will be described later, and it goes without saying that various modifications can be made without departing from the technical ideas of the invention.